The present invention relates generally to disc drives, and more particularly to the mapping of defective sectors in disc drives.
In a disc drive, data is stored on discs. Concentric tracks are defined on each surface of the discs, and each track is further divided into a number of sectors. Each sector represents an addressable location for storing a block of data.
During the manufacturing process, some sectors may be damaged so that data cannot be stored or retrieved from these sectors. Tests are therefore conducted as part of the manufacturing process to determine the validity of each sector. A sector with defects (referred to as xe2x80x9cfactory defectsxe2x80x9d) is not allocated a valid address and therefore will not be utilized. For example, if a particular sector which should be allocated an address of 3 is found to be a defective sector, it is skipped over such that the next sector acquires the address 3. Since the defective sector is not assigned a valid address, data will not be stored in that sector.
When the disc is placed into service, additional sectors on the disc may become defective. Such sectors are referred to in this document as grown defect sectors. One conventional method of dealing with grown defects is to reassign the logical address of the grown defect sector to another sector. For example, a particular sector with the address 4 in Track 1 is found to have a grown defect. The address 4 will be reassigned to a replacement sector usually found on another track, for example, in Track 2. This reassignment of the address is recorded by the controller of the disc drive. In operation, the sectors are read in sequential order of the addresses, therefore the read operation will be interrupted by a first seek operation as the heads move from Track 1 to Track 2 to read from the replacement sector and a second seek operation as the heads move back from Track 2 to Track 1. The movement of the heads to and from the reassigned replacement sector slows down the speed at which data can be read from or written to the discs.
There remains therefore a need for an improved method of dealing with grown defects without compromising the efficiency of the disc drive. It will be evident from the following description that the present invention offers this and other advantages.
According to one aspect of the invention, there is provided a method for eliminating reassignments in a disc drive. A disc drive typically contains at least one disc which is divided into sectors. The method of eliminating reassignments involves copying data stored at one sector (referred to as a moving sector) to another sector (referred to as a moving spare), and assigning the logical address associated with the moving sector to the moving spare.
The elimination process is repeated until the reassignments are eliminated. Verification of the data copied is conducted to ensure data integrity. Furthermore, the elimination process is preferably executed only when the disc drive is in an idle mode. Records are kept and updated as the process is carried out so that the process can be continued even if interrupted.
In another aspect of the invention, there is provided a disc drive with a controller which is configured to perform the steps as described above.